Conventionally, as a brake system for generating a fluid pressure corresponding to a traveling amount of a brake operator, there is known a brake-by-wire type brake system like one described in JP-A-2012-106637.
This brake system has an input unit, a slave cylinder and a fluid pressure control unit. The input unit includes a master cylinder which generates a fluid pressure by means of a piston which is connected to a brake operator and a stroke simulator which gives a pseudo operation reaction force to the brake operator. The slave cylinder includes an electric motor as an electric actuator and a piston which is driven by this electric motor.
In this brake system, the electric motor of the slave cylinder is driven based on a traveling amount of the brake operator, and a fluid pressure is applied to each of wheel brakes by the piston which is driven by the electric motor. In addition, when an anti-lock braking is executed, the fluid pressure control unit is activated to operate to control the fluid pressure applied to the specific wheel brake or brakes. JP-A-2012-106637
The brake system described in JP-A-2012-106637 includes many constituent units, resulting in a problem that the brake system is enlarged in size and becomes complex in architecture.
In the brake system described in JP-A-2012-106637, the tandem type cylinder having two pistons is used for the master cylinder and the slave cylinder, causing a problem that the input unit and the slave cylinder unit are enlarged in size.
In order to avoid the enlargement in size of both the units, for example, in the event that a single type cylinder having a single piston is used for the slave cylinder, in case an abnormal situation where the brake fluid pressure is reduced occurs in one brake system of the two brake systems, there may be fears that the effect of the reduced brake fluid pressure is imposed on the other brake system. This causes a problem that it is difficult to secure the fluid pressure raising performance of the other brake system.
In the brake system described in JP-A-2012-106637, the hydraulic systems are pressurized by driving the slave cylinder, and therefore, the hydraulic systems can be pressurized to reach the high fluid pressure area by increasing the stroke amount of the slave cylinder piston provided in the slave cylinder. Namely, the brake system is obtained which has the fluid pressure raising function which can cope with the required fluid pressure required by the driver by increasing the stroke amount of the slave cylinder piston. However, increasing the stroke of the piston expands the axial length of the cylinder, which enlarges the size of the slave cylinder, calling for an enlargement in size of the brake system.
In the brake system described in JP-A-2012-106637, the hydraulic systems are pressurized by driving the slave cylinder, and therefore, the hydraulic systems can preferably be pressurized to reach the high fluid pressure area by increasing the stroke amount of the slave cylinder piston provided in the slave cylinder. Namely, the brake system is obtained which has the fluid pressure raising function which can cope with the required fluid pressure required by the driver by increasing the stroke amount of the slave cylinder piston. However, increasing the stroke amount of the slave cylinder piston expands the axial length of the cylinder, which enlarges the size of the slave cylinder, calling for an enlargement in size of the brake system. In addition, during an anti-lock braking control, a pressure increasing control to increase a fluid pressure applied to the wheel brakes, a pressure holding control to hold the fluid pressure or a pressure reducing control to reduce the fluid pressure is executed frequently, and therefore, there are possibility that the slave cylinder is enlarged in size so as to secure the brake fluid to be supplied to the wheel brakes.